In recent years, GPS-based navigation systems have grown in popularity and are now widely available in a variety of forms, including different types of vehicle-installed units as well as hand-held portable units. These navigation systems are primarily based on a Global Positioning System (GPS) which was founded by the U.S. Department of Defense and consists of a constellation of 24 satellites working in conjunction with 5 base stations. The satellites orbit the Earth and transmit precise timing data to GPS receivers located on Earth. If strong signals from 3 or more satellites are received, then a latitude and longitude (two-dimensional) position can be determined; if strong signals from 4 or more satellites are received, then a latitude, longitude and altitude (three-dimensional) position can be calculated. Moreover, the accuracy of these navigation systems can be increased through the use of the Wide Area Augmentation System (WAAS), which monitors the satellite data through a collection of base stations and makes signal corrections to provide even more accurate position data.
The success and popularity of vehicle navigation systems has resulted in the development and sale of many different types of systems. For instance, one type of vehicle navigation system currently available is based on telematics. In general, telematics-based vehicle navigation systems utilize a combination of wireless voice and data to communicate between vehicle-installed hardware and a back-end system in order to provide a number of different navigation-related services including turn-by-turn (TBT) spoken directions. In telematics-based systems such as these, the GPS-derived position of the vehicle is compared to road-data provided by the back-end system. The road data not only includes detailed maps of the area(s) in question, but also includes information pertaining to things such as average travel speed classifications, one way streets, highway exit/entrance ramp details, etc. and because the road data is maintained and provided by the back-end system, it is easily and frequently updated. Of course, the vehicle telematics system is typically capable of performing additional, non-navigation related tasks such as those related to providing entertainment, diagnostic or safety functions.
Another type of vehicle navigation system is an autonomous vehicle navigation system mounted on-board the vehicle. These systems use road data that is stored locally at the vehicle such as on a CD or DVD. In this example, the autonomous navigation system compares the position data gathered by the GPS receiver with the road data obtained from the CD or DVD, and the system can then use this information to provide a graphical display at the instrument panel showing a map with the vehicle location. These autonomous systems also allow the driver or other occupant to input a destination address so that the navigation system can provide driving directions graphically as well as turn-by-turn spoken directions. Hence, there is no need to build and maintain a back-end system for supporting the vehicle navigation system.
Each of the aforementioned vehicle navigation systems have certain advantageous qualities, which explains why both types are presently offered on different vehicles. In fact, not only are different types of vehicle navigation systems sometimes offered on the same vehicle, in some cases a vehicle can come equipped with multiple navigation systems so that the user has the ability to select the one they would like to use.